Rotor cores for use in rotary electric machines are usually constructed of a stack of thin steel sheets. Since the rotor cores are of a hollow cylindrical shape, each of the thin steel sheets is cut from a steel sheet into an annular shape. However, as the scrap cut off from inside the annular sheet is wasted, use of the steel sheet suffers a low yield and is not economical.
In an attempt to utilize the steel sheet more extensively, there has been proposed a rotor including a rotor core which comprises a plurality of circumferentially separate core segments each in the form of an annular thin steel sheet (see, for example, Japanese Laid-Open Patent Publication No. 2000-224790). Each of the core segments has teeth and grooves on its circumferentially opposite ends. The core segments are interconnected into an annular rotor core with the teeth fitting in the grooves.
The core segments also have axial holes defined therein. Reinforcing fastening support members such as rivets or bolts are inserted through the axial holes and have opposite ends fixed to side plates, thereby securing the core segments to the side plates. However, the core segments secured to the side plates by the rivets or the bolts are not strong enough to be used in rotary electric machines which undergo large torques. Accordingly, the separate core segments tend to have difficulty being securely and stably used in rotary electric machines.
Japanese Laid-Open Patent Publication No. 2005-210790 discloses a rotary electric machine including a rotor which comprises a boss and a rotor core which are integrally formed of aluminum by casting. In the disclosed rotary electric machine, the boss is firmly coupled to the rotor core.